Bug 1846890 - Fix busted cron-system-symbols Decision tasks, r=jlorenzo

The move to `from-deps` changed the dependency edge name from `build` to
`system-symbols`. Apparently this is what the first path segment in an
`artifact-reference` is.

We should probably change the separator to a `:` or something here.

Differential Revision: https://phabricator.services.mozilla.com/D185297

taskcluster/ci/system-symbols-reprocess/kind.yml

@@ -38,7 +38,7 @@ jobs:
                 DUMP_SYMS: "/bin/false"
         run:
             using: run-task
-            command: {artifact-reference: "${MOZ_FETCHES_DIR}/symbol-scrapers/reprocess.sh <build/public/build/target.crashreporter-symbols.zip>"}
+            command: {artifact-reference: "${MOZ_FETCHES_DIR}/symbol-scrapers/reprocess.sh <system-symbols/public/build/target.crashreporter-symbols.zip>"}
         fetches:
             fetch:
                 - symbol-scrapers

taskcluster/ci/system-symbols-upload/kind.yml

@@ -28,7 +28,7 @@ jobs:
                 SYMBOL_SECRET: "project/releng/gecko/build/level-{level}/gecko-symbol-upload"
         run:
             using: mach
-            mach: {artifact-reference: "python toolkit/crashreporter/tools/upload_symbols.py <build/public/build/target.crashreporter-symbols.zip> --ignore-missing"}
+            mach: {artifact-reference: "python toolkit/crashreporter/tools/upload_symbols.py <system-symbols/public/build/target.crashreporter-symbols.zip> --ignore-missing"}
             sparse-profile: upload-symbols
         scopes:
             - secrets:get:project/releng/gecko/build/level-{level}/gecko-symbol-upload